JP3678033B2 - Engine combustion start control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for controlling an engine of a vehicle such as an automobile, and more particularly to a hybrid vehicle having a fuel cut return, an engine and a motor as a driving force source of the vehicle, or an idle stop that automatically stops the engine during idling. The present invention relates to a vehicle engine combustion start control method suitable for automatic engine start in a vehicle.
[0002]
[Prior art]
For example, a technique described in Japanese Patent Application Laid-Open No. 6-17727 is known as a technique related to automatic engine starting while the motor is running in a hybrid vehicle equipped with an engine and a motor as a power source for the vehicle. In this conventional example, an engine is connected to a motor directly connected to a drive system of a vehicle via a clutch, and when starting the engine from running of the motor alone, the clutch is connected and the output of the motor is increased. This is corrected to prevent the occurrence of a shock when starting the engine.
[0003]
[Problems to be solved by the invention]
However, the above-described conventional example compensates for a phenomenon in which a part of the output of the motor is consumed for starting the engine at the time of the automatic engine start and the vehicle driving torque drops by increasing the output of the motor. There is a problem that it is not possible to sufficiently suppress the shock that occurs before and after the start of engine combustion.
[0004]
That is, in the above-described conventional example, under the situation where the clutch is connected and the engine starts to rotate, the engine generates a contracted torque that becomes resistance to the running of the vehicle, but when the engine starts combustion from this state, the engine There is a problem that a so-called positive torque that contributes to running of the vehicle is generated, and a shock due to a sudden torque step occurs.
[0005]
This shock can be transmitted to the vehicle body through the drive system of the vehicle and cause discomfort to the passengers. In particular, the start of combustion of the engine that causes such a shock is not generated by the driver's conscious operation, and thus the above shock is easily felt by the driver.
[0006]
In addition, the shock at the time of automatic engine start in an idling stop car is not much different from the start at the key operation, but the shock at the automatic engine start that does not depend on the driver's conscious operation is felt more greatly. There is a problem similar to that of the hybrid vehicle described above.
[0007]
Such a problem occurs not only in the hybrid vehicle as described above, but also in a vehicle equipped with a device that cuts the fuel supply to the engine when the vehicle decelerates, when returning from the fuel supply cut state.
[0008]
Further, if the engine output torque is suppressed as much as possible at the start of combustion of the engine, the shock can be reduced. However, the acceleration immediately after the start of engine combustion cannot be performed smoothly only by suppressing the torque. Therefore, it is conceivable to increase the torque immediately after the start of combustion to respond to the acceleration request, but there is a problem of so-called transient NOx that temporarily generates a large amount of NOx.
[0009]
Accordingly, an object of the present invention, when the start of the fuel supply of the engine F while rotating the engine to start combustion of the engine, to ensure acceleration performance while suppressing the occurrence of shock, also, transient An object of the present invention is to provide an engine combustion start control method capable of suppressing N0x.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problems and achieve the object, the engine combustion start control method of the present invention starts fuel supply to the engine by starting the fuel supply to the engine while the engine is rotated. In the engine combustion control method, the engine is configured to be switchable between a lean operation mode in which the engine is operated at a lean air-fuel ratio and a normal operation mode in which the engine is operated at an air-fuel ratio that is higher than the air-fuel ratio in the lean operation mode, The lean operation mode is a compression lean operation mode in which fuel is supplied to the combustion chamber during the compression stroke and is operated at a lean air-fuel ratio. The normal operation mode supplies fuel to the combustion chamber during the intake stroke and performs the compression. It is a mode that is operated at an air-fuel ratio that is deeper than the air-fuel ratio in the lean operation mode, and at the start of the fuel supply, the compression lean operation mode is selected, One, the timing at which the engine speed while the fuel is injected more than a predetermined rotation speed, the ignition timing and fuel injection timing at the start of the fuel supply, stable combustion is possible within a region and brake mean effective pressure of the engine is low Drive at a retarded angle .
In the present invention, the engine includes exhaust gas recirculation means for returning a part of exhaust gas to the intake system, and the exhaust gas recirculation means is driven before the engine is switched to the normal operation mode after being driven in the compression lean operation mode. Then, exhaust gas may be added to the combustion chamber. In this case, part of the exhaust gas has already been introduced into the air-fuel mixture immediately after switching from the compression / lean operation mode to the normal operation mode. For this reason, it is possible to suppress transient NOx that occurs temporarily immediately after switching from the lean operation mode to the normal operation mode.
[0011]
Since the engine is operated in the lean operation mode that is operated at the lean air-fuel ratio at the start of fuel injection for starting engine combustion, it is possible to suppress the output torque of the engine at the start of combustion. For this reason, it is possible to efficiently suppress the output torque of the engine at the start of combustion and suppress the occurrence of shock at the start of combustion of the engine.
[0012]
In addition, the vehicle acceleration can be ensured by switching from the lean operation mode to the normal operation mode. As a preferred mode, in the lean operation mode, it is desirable to inject fuel during the compression stroke of the engine. In this case, even when a small amount of fuel is injected, stratified combustion is possible in which a relatively thick layer of fuel is formed in the vicinity of the spark plug, and stable combustion of the engine is possible even with a lean mixture of fuel. For this reason, it is possible to efficiently suppress the output torque of the engine at the start of combustion and effectively suppress the occurrence of shock.
[0013]
Furthermore, at least one of the ignition timing and the fuel injection timing at the start of combustion,
It is desirable to set a time later than the so-called MBT (Minimum Spark Advance for Best Torque) in which the torque output from the crankshaft is maximum within the stable combustion region of the engine. In this case, it is possible to further suppress a sudden increase or decrease in output torque that occurs at the start of engine combustion.
[0014]
In addition, when at least one of the ignition timing at the start of combustion and the fuel injection timing is set to a timing later than the MBT in the lean operation mode, the ignition timing and It is desirable to gradually advance at least one of the fuel injection timings so as to gradually approach the MBT. In this case, the output torque gradually increases from the start of combustion, and a sudden change in the output torque can be further suppressed.
[0015]
Also, after starting combustion of the engine, it is desirable to gradually advance the ignition timing to increase the output torque, and then switch to the normal operation mode. In this case, the vehicle can smoothly shift to a state where acceleration response of the vehicle is high. it can. Accordingly, the response after the accelerator pedal is operated when accelerating or the like is improved, and the uncomfortable feeling given to the driver can be suppressed.
[0016]
Further, immediately after switching from the lean operation mode to the normal operation mode, it is desirable to set the ignition timing later than the MBT in the normal operation mode. in this case,
The output torque of the engine immediately after switching to the normal operation mode is suppressed, and it is possible to more reliably suppress a relatively rapid increase / decrease in torque when switching from the lean operation mode to the normal operation mode. Become.
[0017]
In addition, when the lean operation mode is switched to the normal operation mode, it is possible to suppress the generation of NOx by driving the exhaust gas circulation means at the same time or before switching.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
[0019]
As shown in FIG. 1, a vehicle that travels by combining an engine as an internal combustion engine and a motor, a so-called hybrid vehicle 1, includes a spark ignition type engine 2, a motor / generator 3 that functions as a motor and a generator, Wheels 4 and 4 as drive wheels, accelerator opening detection means 5, vehicle speed detection means 6, engine speed detection means 7, crank angle detection means 16, key switch 22, and ECU ( Electronic Control Unit) 8 etc.
[0020]
The engine 2 includes an injector 10 as fuel injection means for directly injecting fuel into the combustion chamber, an EGR device 15 as exhaust gas recirculation means, and the like. The injector 10 is configured to be able to inject fuel directly into the combustion chamber of the engine 2. The injector 10 has a configuration in which the amount of fuel injected per unit time is substantially constant, and the amount of fuel injected into the combustion chamber is controlled by controlling the injection time from the ECU 8 or the like.
[0021]
The EGR device 15 has a function of extracting a part of the exhaust gas and returning the exhaust gas into a passage of an intake system such as an intake port. The EGR device 15 is configured so that the operation of an EGR valve (not shown) is controlled by the ECU 8 and the timing for returning a part of the exhaust gas into the passage of the intake system is controlled.
[0022]
The engine 2 includes a compression lean operation mode as a lean operation mode in which a relatively small amount of fuel is directly injected from the injector 10 into the combustion chamber during the compression stroke and is operated at a predetermined lean air-fuel ratio (30 to 50), and intake air and fuel is supplied into the combustion chamber during stroke predetermined lean air-fuel ratio and the intake lean mode operating at (20 to 23), fuel is supplied into the combustion chamber during the intake stroke rich or the stoichiometric air-fuel ratio (12 The normal operation mode operated in 14.7) can be switched.
[0023]
The engine 2 is provided with an ignition device 9, and the ignition timing of the engine 2 is controlled by controlling the operation timing by the ECU 8.
[0024]
The engine 2 has an output shaft 11 connected to the motor / generator 3 via a clutch 12. The operation of the clutch 12 is controlled by the above-described ECU 8, and the transmission of power between the engine 2 and the motor / generator 3 is connected and separated.
The engine 2 and the motor / generator 3 are connected to an axle 14 and a pair of left and right wheels 4 and 4 through a differential gear 13 and the like.
[0025]
Further, a starting clutch 21 is provided between the motor / generator 3 and the differential gear 13, and the starting clutch 21 is normally in a contact state, and is stopped when the engine 2 is stopped or when the engine 2 is stopped. It is in a disconnected state. The wheels 4 and 4, the differential gear 13, and the axle 14 constitute the drive system members described in this specification.
[0026]
The motor / generator 3 has both functions of an electric motor and a generator. When functioning as an electric motor, the motor / generator 3 drives the wheels 4 and 4 through the differential gear 13 and the axle 14 and generates power. When functioning as a machine, power is generated using the driving force transmitted from the engine 2 or the axle 14 or the like, and a battery (not shown) is charged.
[0027]
The accelerator opening detection means 5 detects an accelerator pedal on / off operation and an operation amount, and outputs an accelerator opening signal Ac to the ECU 8. The vehicle speed detection means 6 is a known vehicle speed sensor or the like that can detect the rotation of the wheel 4 and the like, and outputs a vehicle speed signal Vs to the ECU 8. The engine speed detection means 7 detects the speed of the crankshaft of the engine 2 and outputs an engine speed signal Ne to the ECU 8. The crank angle detection means 16 detects the crank angle of the engine 2 within a range of 720 degrees from the crankshaft angle and the camshaft angle, and outputs a crank angle signal Ca to the ECU 8. The key switch 22 detects an engine start request signal Ky by a driver's key operation.
[0028]
The ECU 8 controls operations of the motor / generator 3, the ignition device 9, the clutch 12, the starting clutch 21, the injector 10, the EGR device 15, and the like based on the signals Ac, Vs, Ne, Ca, Ky and the like described above.
[0029]
First, the outline of the start control for the engine 2 will be described. When the engine start request is made based on the operation of the key switch 22, that is, when the start is requested by the driver's will, the ECU 8 starts the engine. The engine is started in the normal operation mode giving priority to the performance. When the ECU 8 automatically requests engine start regardless of the operation of the key switch 22, that is, when the engine is automatically started regardless of the driver's conscious operation, priority is given to shock suppression at the time of start. Then, the engine is started in the compression lean operation mode.
[0030]
Next, details of the case where the engine is automatically started will be described.
[0031]
The ECU 8 is an injector for stopping the fuel injection into the combustion chamber of the engine 2 when the hybrid vehicle 1 can travel by the motor / generator 3 alone, when the engine 2 is decelerated even when the engine 2 is operating, or when traveling downhill. 10 is controlled. The ECU 8 separates the engine 2 from the drive system member by the clutch 12 in a state where the fuel injection from the injector 10 is stopped. The vehicle travels using only the output of the motor / generator 3 with the engine 2 stopped. For example, when the accelerator pedal is operated and acceleration greater than the output of the motor / generator 3 is requested in the traveling state of the motor / generator 3 alone, the engine 2 is connected to the drive system member by the clutch 12 to enter the combustion chamber. The injector 10 is controlled to start the fuel supply, and the ignition device 9 is operated to start the engine 2.
[0032]
When starting fuel injection into the combustion chamber, the ECU 8 operates the engine 2 in the above-described compression / lean operation mode. At this time, the ECU 8 delays at least one of the fuel injection timing and the ignition timing as compared with an MBT advance angle which will be described later. In the present embodiment, as shown in FIG. 2, the ECU 8 controls the injector 10 and the ignition device 9 by delaying both the fuel injection timing and the ignition timing.
[0033]
In FIG. 2, the horizontal axis indicates the end timing of fuel injection, and the injection end timing is delayed toward the left in the figure and the injection end timing is advanced toward the right. The vertical axis indicates the ignition timing. The ignition timing is delayed as it goes downward in the figure, and the ignition timing is advanced as it goes upward. These injection end timing and ignition timing indicate the rotation angle of the crankshaft.
[0034]
In FIG. 2, curves Pe 1, Pe 2, Pe 3 and Pe 4 indicate the net average effective pressure corresponding to the output torque of the engine 2. These curves Pe1, Pe2, Pe3, and Pe4 increase in order.
[0035]
A region R surrounded by a two-dot chain line P in FIG. 2 indicates a region where the engine 2 at the time of compression lean operation stably burns without misfiring. The region outside this region R is the region where the engine 2 is It is an area where it is difficult to achieve stable combustion due to misfire.
[0036]
As shown in FIG. 3, when starting the engine 2, the ECU 8 first operates an accelerator pedal or the like to input an accelerator opening signal Ac from the accelerator opening detecting means 5, and the clutch 12 is connected to the engine 2 and the motor. / Power transmission to / from generator 3 is connected. When the transmission of power of the clutch 12 is connected, the crankshaft of the engine rotates together with the drive system member of the vehicle such as the axle 14 and the motor / generator 3.
[0037]
When the engine speed starts to increase due to the clutch 12 being connected and the engine speed signal Ne exceeds a predetermined speed N such as 1500 rpm, the injection end timing is within the region R where stable combustion of the engine 2 is possible. As shown in FIG. 2, the net average effective pressure is low as a relatively slow predetermined retarded position where the ignition timing is in the vicinity of the minimum value. And ignite.
[0038]
Thereafter, the fuel injection timing and ignition timing are gradually advanced. The fuel injection timing and the ignition timing are shifted to the timing indicated by the point D2 in FIG. 2 earlier than the timing indicated by the point D1 with the passage of time, and further the fuel at the timing indicated by the point D3 in FIG. Is injected and ignited. In the process of advancing the fuel injection timing and the ignition timing, the net average effective pressure gradually increases and the output torque of the engine 2 gradually increases.
[0039]
Note that a point D3 shown in FIG. 2 indicates a timing at which the so-called MBT (Minimum Spark Advance for Best Torque) advance angle at which the torque output from the crankshaft of the engine 2 during the compression lean operation is maximized. Show.
[0040]
Thus, the ECU 8 sets the fuel injection end timing and the ignition timing corresponding to the fuel injection timing at the start of fuel supply for starting the combustion of the engine 2 to a predetermined delay delayed from the MBT advance angle as indicated by the point D1. The timing is at the corner position.
[0041]
Thereafter, the ECU 8 switches to the normal operation mode in which fuel is injected from the injector 10 into the combustion chamber during the intake stroke of the engine 2. At the time of switching to the normal operation mode with a rich air-fuel ratio, the amount of fuel injected from the injector 10 is increased, resulting in an increase in the output torque. At the same time, the ignition timing is predetermined from the MBT advance angle in the normal operation mode. Therefore, the sudden increase in output torque is suppressed. Thereafter, the injection amount is increased and the ignition timing is advanced to increase the output torque. Further, the ECU 8 operates the EGR device 15 immediately before shifting to the normal operation mode. Exhaust gas is introduced into the air-fuel mixture burned in the normal operation mode.
[0042]
Note that the delay time (T in FIG. 3) from when the accelerator pedal is depressed to when the fuel injection amount is increased does not become a problem of responsiveness within 1 second.
As shown in FIG. 3, the output torque is extremely low at first, and then gradually increases, so that smooth acceleration can be obtained while suppressing the occurrence of shock.
[0043]
FIG. 4 shows the result of measuring the change in the average effective pressure corresponding to the output torque of the engine 2 with respect to the change in the intake pipe pressure when the combustion condition of the engine 2 is changed.
[0044]
In the measurement, when the engine 2 is combusted by the combustion control method of the ECU 8 described in the present embodiment (hereinafter referred to as the present invention) indicated by a black square in FIG. 4 and each of the comparative examples A to D The average effective pressure was measured.
[0045]
The comparative example A indicated by the solid line in FIG. 4 shows the average effective pressure when the fuel supply to the engine 2 is stopped and the clutch 12 is connected and the engine 2 rotates (when the engine 2 is in the motoring state). Yes. A comparative example B indicated by white circles in FIG. 4 shows the average effective pressure when the fuel-air mixture in the combustion chamber injects an amount of fuel that is a stoichiometric air-fuel ratio, so-called stoichiometric, and the ignition timing is MBT advance.
[0046]
The comparative example C indicated by a black circle in FIG. 4 is an average effective when the so-called ignition retard is performed in which the amount of fuel that becomes the stoichiometric mixture is injected and the ignition timing is delayed in the region R in which stable combustion of the engine 2 is possible. Indicates pressure. A comparative example D indicated by a triangle in FIG. 4 indicates an average effective pressure when the engine 2 is operated in the above-described intake lean operation mode in which fuel is injected during the intake stroke of the engine 2 and ignition retard is performed.
[0047]
According to FIG. 4, the product of the present invention has a difference from Comparative Example A (corresponding to the state before the start of combustion) from about 1/4 to about 1/2 compared to Comparative Examples B to D and the like. ing.
For this reason, the product of the present invention has a step difference in the output torque of the engine 2 when starting the combustion of the engine 2 by operating an accelerator pedal or the like to accelerate from a state where the vehicle travels only with the output of the motor / generator 3, for example. It is clear that it can be suppressed.
[0048]
According to the present embodiment, the EGR device 15 is driven immediately before switching to the normal operation mode. For this reason, exhaust gas has already been added to the air-fuel mixture immediately after switching to the normal operation mode. For this reason, it becomes possible to suppress the transient NOx generated immediately after switching to the normal operation mode.
[0049]
Further, since the output torque of the engine 2 when starting the combustion of the engine 2 can be suppressed from the state where the hybrid vehicle 1 travels only with the output of the motor / generator 3, the shock difference is suppressed by suppressing the torque step before and after the start of combustion. Can be suppressed.
[0050]
In the compression stroke of the engine 2, after a minimum amount of fuel is injected and the ignition timing is delayed to start combustion, the fuel injection timing and the ignition timing are gradually advanced in the lean operation mode, and the output output by the engine 2 Increase torque. Then, since the lean operation mode is switched to the normal operation mode of the stoichiometric air-fuel ratio or the rich air-fuel ratio, it is possible to smoothly shift to acceleration after the combustion of the engine 2 is started. For this reason, it becomes possible to improve the response characteristics when accelerating and to suppress the uncomfortable feeling given to the driver and the like.
[0051]
Further, when switching from the lean operation mode to the normal operation mode, the ignition timing is retarded to suppress the output torque of the engine 2. For this reason, it is possible to suppress torque fluctuations that occur when switching to the normal operation mode, and it is possible to further suppress light shocks given to passengers and the like.
[0052]
In the above-described embodiment, the so-called hybrid vehicle 1 including the engine 2 and the motor / generator 3 is described. However, the present invention is not limited to the hybrid vehicle. For example, during normal vehicle deceleration traveling or downhill traveling When the fuel injection is temporarily stopped, the fuel injection can be resumed.
[0053]
In the embodiment described above, the EGR device 15 is driven immediately before switching to the normal operation mode, but the EGR device 15 may be driven simultaneously with switching to the normal operation mode.
[0054]
Further, in the present invention described above, the vehicle is not limited to the direct injection type engine in which fuel is directly injected into the combustion chamber, but is provided with a so-called lean burn engine capable of switching between the above-described lean operation mode and normal operation mode. Needless to say, this method can be applied to the fuel control method. Further, the operation mode at the start of combustion may be an intake lean operation mode.
[0055]
【The invention's effect】
According to the first aspect of the present invention , the occurrence of shock at the start of engine combustion can be suppressed by starting combustion in the lean operation mode. According to the second aspect of the present invention, exhaust gas recirculation is performed at the same time or before switching from the lean operation mode to the normal operation mode after the start of combustion, so that transient NOx generated immediately after switching to the normal operation mode is suppressed. It is possible to ensure acceleration while.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a hybrid vehicle as one embodiment of the present invention.
FIG. 2 is a view showing a relationship between fuel injection timing and ignition timing at the start of combustion according to the embodiment.
FIG. 3 is a time chart showing a processing flow at the start of combustion according to the embodiment;
FIG. 4 is a view showing an average effective pressure between the engine of the embodiment and a comparative example.
[Explanation of symbols]
1 ... Hybrid vehicle (vehicle)
2 ... Engine 4 ... Wheel (drive system member)
13 ... Differential gear (drive system member)
14 ... Axle (drive system member)
15 ... EGR device (exhaust gas recirculation means)

Claims (2)

In the engine combustion control method for starting the combustion of the engine by starting the supply of fuel to the engine with the engine rotated.
The engine is
A lean operation mode operated at a lean air-fuel ratio;
The normal operation mode that is operated at an air-fuel ratio that is deeper than the air-fuel ratio in the lean operation mode is configured to be switchable,
The lean operation mode is a compression lean operation mode in which fuel is supplied to the combustion chamber during a compression stroke and is operated at a lean air-fuel ratio, and the normal operation mode is configured to supply fuel to the combustion chamber during an intake stroke. It is a mode that is operated at an air-fuel ratio that is deeper than the air-fuel ratio in the compression lean operation mode,
When the fuel supply is started, the compression lean operation mode is selected, the fuel is injected at an engine speed equal to or higher than a predetermined speed, and the fuel injection timing and the ignition timing at the start of fuel supply are determined based on stable combustion of the engine. An engine combustion start control method, characterized in that the engine is operated at a retarded angle so that the net average effective pressure falls within a possible range . In the engine combustion control method for starting the combustion of the engine by starting the supply of fuel to the engine with the engine rotated.
The engine is
A lean operation mode operated at a lean air-fuel ratio;
The normal operation mode that is operated at an air-fuel ratio that is deeper than the air-fuel ratio in the lean operation mode is configured to be switchable,
The lean operation mode is a compression lean operation mode in which fuel is supplied to the combustion chamber during a compression stroke and is operated at a lean air-fuel ratio, and the normal operation mode is configured to supply fuel to the combustion chamber during an intake stroke. It is a mode that is operated at an air-fuel ratio that is deeper than the air-fuel ratio in the compression lean operation mode,
The engine includes exhaust gas recirculation means for returning a part of the exhaust gas to the intake system;
At the start of fuel supply, the compression lean operation mode is selected, and fuel is injected at an engine speed equal to or higher than a predetermined speed,
An engine combustion start control method comprising: driving the exhaust gas recirculation means to add exhaust gas into the combustion chamber before switching the engine to the normal operation mode after being driven in the compression lean operation mode.

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